The present invention relates to a magnetic disk apparatus and a servo signal recording method and more specifically to a servo write operation that records a reference clock signal used as a timing reference for writing a servo signal without using a dedicated clock head in a magnetic disk apparatus such as a hard disk drive.
In magnetic disk apparatus, several tens to more than several hundreds of servo signals (servo sectors) are placed on a recording surface of the disk in each cyclic movement (revolution) for position detection of the head.
In a normal servo write process, as described in JP-A-2000-123509, a dedicated head called a clock head is used to record a clock track on the recording surface to define a circumferential position of each servo sector. Reading this clock track produces a clock signal representing a position of the servo sector in a disk rotating direction (refer to reference 1).
Another proposed method, as described in U.S. Pat. No. 5,519,546, involves producing a clock signal by using a normal head of a magnetic disk apparatus without using a dedicated head.
The method described in the U.S. Pat. No. 5,519,546 requires a head of the magnetic disk apparatus to read a part of the clock track already recorded on the disk surface and at the same time write a new track to connect them in a circumferential direction. With magnetoresistive heads currently in use on general magnetic disk apparatus, since a writing element and a reading element are separated from each other, a problem arises that a newly recorded track does not connect to the already recorded track.
Further, conventional clock tracks, such as those described in JP-A-2000-123509, are generally managed strictly in such a manner that the number of clock bits in each revolution can be divided by the number of sectors. This makes it necessary to perform the writing operation again if a bit length of a write connecting portion in one revolution fails to fall within a certain range.
However, in cases where a head of a magnetic disk apparatus available in recent years, whose writing or reading element is only several hundred nm wide, is used to record tracks, there is a fear that the writing element may not be able to be positioned correctly on the clock track, failing to perform the rewriting operation described above.